Posted
by
timothy
on Wednesday September 30, 2009 @02:12PM
from the for-the-journal-of-sensors-and-transducers dept.

cremeglace writes "Scientists at the University of Colorado at Boulder have found a use for GPS besides finding restaurants or the occasional road-that-doesn't-exist: it can be used to measure snow depth. The new technique, which takes advantage of distortions of the GPS signal after it reflects off the snowpack, may potentially improve weather forecasts by allowing meteorologists to track snowfall patterns. ScienceNOW has the story, which one geophysicist describes as 'a classical case of one person's noise becoming another person's signal.'"

There already exists a tool for measuring snow depth. Its called a ruler. There are imperial (yardstick) and metric varieties.

Another useful thing is a shovel, you can dig yourself out, and cut a path to the part of the road that has been plowed.

A cellphone is very useful too, you can call work and tell them you are stuck in a snowdrift and won't be in today. Don't forget to get out of the car before calling though, since in some places its illegal to use a cellphone in a car.

TFA is talking about using an existing network of 1100 GPS receivers currently tracking plate tectonics to also track snowfall, without any additional equipment and without interfering with their current operation.

This not about using your Garmin to find out how much snow is in your front yard.

Of course, it's accidental radar altimetry, rather than a dedicated instrument. Neat hack.

Um, no. It's not like SRA, apart from the use of a satellite, RF radiation, and the measurement of a distance.

Main differences:

This system is bistatic; SRA is monostatic.

This system uses an (almost) isotropic antenna to collect radiation from pretty much everywhere; SRA uses a high gain antenna to survey only a very narrow target swathe.

This system measures the effective speed of light in a multipath environment, assuming the multipath reflectors are at fixed distances; SRA measures the distance of multipath reflectors, assuming the effective speed of light is fixed.

Disclaimer: I work on satellite synthetic aperture radar, which is different again, and my knowledge of SRA isn't comprehensive.

not really, no. Satellite radar altimetry is just simple time domain reflectometry. Send a pulse of light, microwaves, whatever and use the elapsed time (along with knowledge of the speed of light) until hearing the echo to determine distance, subtract ephemeris data describing the satellite's orbit and get alitmetry out. Done. That is not at all what is being done here. So far as I know, there is no way of directly measuring snow depth from a satellite. If you're in orbit at 400 miles up trying to measure

Does it account for the fact that almost-melting snow will layer more compactly then sub-30C snow which is extremely crystalline and less likely to make compact layers?

Disclaimer: I haven't RTFPaper. I'll do that tomorrow, since it's of professional interest. What follows is guesswork.

Imagine you've got an RF antenna on a flat surface. Above the flat surface is a layer of snow of constant thickness h. Now place at least three point RF sources at different angles theta and distances r from the antenna. Assume that all the sources lie above the snow.

Now, the distance that each RF signal must travel through the snow, x, will depend on d and theta, but not on r. You'll find

If you have any wind when the snow falls, you're going to have drifting which makes such measurements useless.

I take great exception to this statement and your dismissive attitude towards their results. Drifting will introduce uncertainty into the measurements, and that uncertainty can be estimated and accounted for. It by no means makes the measurements 'useless.' Scientific experiments are never carried out in ideal environments, and the mathematical methods that have been developed to extract information from poor-quality data are truly amazing.

This did cross my mind as well, although it should not be a replacement for proper use of an avy probe, more information is never a bad thing. Better yet, it would be great to use the variations in snow-pack density to predict the snow stability. Stupid and/or lazy people are everywhere, even skiing in the backcountry and this could help save their lives.

All jokes aside, the western US and Canada are completely reliant on snow pack for water supply. No snow, and you have severe drought. Knowing what is happening with snow pack is a huge issue there and in may other places in the world.

We already know, as there are manual snow course surveys and snow pillows all over the place. Here is a list of 400 or so (some are historic and no longer sampled) snow courses [gov.bc.ca] in BC. Many of those get visited every two or four weeks from Jan-Feb through June each year.

I've done the surveys, and you need to measure both snow depth, and moisture content. The process of manual measurement hasn't changed in decades - you drop a metal tube into the ground, pull it up, dig out the soil, measure the weight of th

Interestingly, people have used GPS to measure temperatures in the Earth's atmosphere. The idea is to precisely measure the Doppler shift of the GPS satellite signal. This is modified by the refraction of radio waves through the atmosphere. Atmospheric refraction is governed by the density of air, which in turn depends on its temperature. Thus, radio occultation [wikipedia.org] measurements can be used to infer (a convolved integral of) the air temperature along the line-of-sight. Many such measurements can be used to